(1) Field of the Invention
This invention relates to a method for fabricating a semiconductor device and, more particularly, to a method for fabricating a semiconductor device in which nickel silicide (NiSi) is used.
(2) Description of the Related Art
Conventionally, cobalt silicide has been used for forming a gate electrode, a source electrode, and a drain electrode of a metal oxide semiconductor field-effect transistor (MOSFET). With MOSFETs in which gate length is below 40 nm, however, variation in the resistance of thin gate lines of cobalt silicide sharply becomes great. On the other hand, even if gate length is below 40 nm, the resistance of thin gate lines of nickel silicide is stable. Accordingly, attention has been riveted on nickel silicide.
However, the thermal stability of nickel silicide is low, so nickel silicide easily agglomerates at a temperature of about 500° C. (see M. Tinani, et al., “In situ real-time studies of nickel silicide phase formation”, J. Vac. Sci. Technol. B 19(2), 376 (2001)). In anh interconnection process performed after a salicide process for forming nickel silicide, the nickel silicide is exposed to a temperature of about 400° C. for a long period of time. As a result, the nickel silicide agglomerates. Therefore, high-resistance nickel disilicide (NiSi2) or the like is formed. In addition, the nickel disilicide is in proximity to a pn junction and junction leakage occurs.
To suppress such agglomeration of nickel silicide, techniques for doping nickel with impurities, such as platinum (Pt), palladium (Pd), fluorine (F), nitrogen (N), tantalum (Ta), tungsten (W), or carbon (C), have conventionally been proposed (see D. Mangelinck, et al., “Effect of Co, Pt, and Au additions on the stability and epitaxy of NiSi2 films on (111)Si”, J. Appl. Phys., 84, 2583 (1988); D. Z. Chi, et al., “Addressing Materials and Process-Integration Issues of NiSi Silicide Process Using Impurity Engineering”, The 4th International Workshop on Junction Technology, pp. 113 (2004); C.-C. Wang, et al., “Formation of NiSi-Silicided p+n Shallow Junctions Using Implant-Through-Silicide and Low-Temperature Furnace Annealing”, J. Electrochem. Soc., 150, G557 (2003); J.-G. Yun, et al., “Abnormal Oxidation of Nickel Silicide on N-Type Substrate and Effect of Preamorphization Implantation”, Jpn. J. Appl. Phys., 43, 10, 6998 (2004); J. A. Kittl, et al., “Applications of Ni-based suicides to 45 nm CMOS and Beyond”, Mat. Res. Soc. Symp. Proc. 810, C2. 1. 1 (2004); W. Huang, et al., “Effect of a thin W interlayer on the thermal stability and electrical characteristics of NiSi film”, J. Vac. Sci. Technol. B23, 2304 (2005); and K.-W. Do, et al., “Formation of Low-Resistivity Nickel Silicide with High Temperature Stability from Atomic-Layer-Deposited Nickel Thin Film”, Jpn. J. App. Phys. 45 B 2975 (2006)).
Furthermore, it is reported that a thermal stability is improved by depositing a nickel film over a silicon substrate and implanting hydrogen ions in the nickel film with hydrogen plasma (see C.-J. Choi, et al., “Effects of Hydrogen Implantation on the Structural and Electrical Properties of Nickel Silicide”, J. Electrochem. Soc., 149, G517 (2002)). According to this report, a nickel film with a thickness of 30 nm is deposited over a silicon substrate, hydrogen ions are implanted in the nickel film, and annealing is performed. By doing so, nickel silicide is formed. According to C.-J. Choi, et al., “Effects of Hydrogen Implantation on the Structural and Electrical Properties of Nickel Silicide”, J. Electrochem. Soc., 149, G517 (2002), the principal factor in the improvement of the thermal stability of nickel silicide is that the grain size of nickel silicide becomes small by adopting the above method.
By the way, usually temperature at which silicide agglomerates rises in proportion to film thickness. That is to say, a thick silicide film is hard to agglomerate. The reason for this is that grain boundary energy lowers in proportion to film thickness. From the viewpoint of the process technology of fabricating transistors the size of which is 90 nm or less, however, junction depth is 100 nm or less. Accordingly, it is desirable that the thickness of a silicide film should be about 20 nm or less. If such a thin silicide film is formed, nickel silicide agglomerates even at a temperature lower than or equal to 500° C. As a result, the improvement of the thermal stability of nickel silicide has become more and more necessary.
Japanese Unexamined Patent Publication No. 58-213465 discloses the use of hydrogen plasma at the time of forming a Schottky barrier diode on polycrystalline silicon. If this technique is used, hydrogen combines with dangling bonds in polycrystalline silicon, the band structure of the polycrystalline silicon becomes close to that of single crystal silicon, and a Schottky barrier diode having good characteristics is obtained.
In addition, Japanese Unexamined Patent Publication No. 2004-128501 discloses performing ammonia (NH3) plasma treatment for the purpose of improving adhesion between nickel silicide, which is an electrode, and silicon nitride (SiN), which is an etching stopper.
However, the size of transistors has become minuter in recent years and the thermal stability of nickel silicide cannot be improved sufficiently by conventional techniques.